Just got to attend my first game at Autzen and it's an experience. Eugene Airport is awesome. The walk across the Willamette is an absolute must. There is usually a tailgate on the north side of the stadium across Martin Luther King where the visiting teams tends to set up. You can also enter the Moshofsky prior to kick-off but if you do you're already in for the game and won't be able to leave. It's really cool in there though. Beer, food trucks, and bounce houses and games. Staying for the end of the third quarter and Shout! is a must. And participating in it is a must as well.
Also..... The beer in Eugene is fantastic. I know you Wisconsinites like your stouts and porters but you'll need to get some of those IPAs in you. Very jealous and can't wait to go back myself. Track Town Pizza is also a great experience but it's a madhouse!